Class::Struct exports a single function, struct. Given a list of element names and types, and optionally a class name, struct creates a Perl 5 class that implements a "struct-like" data structure.

The new class is given a constructor method, new, for creating struct objects.

Each element in the struct data has an accessor method, which is used to assign to the element and to fetch its value. The default accessor can be overridden by declaring a sub of the same name in the package. (See Example 2.)

The first and second forms explicitly identify the name of the class being created. The third form assumes the current package name as the class name.

An object of a class created by the first and third forms is based on an array, whereas an object of a class created by the second form is based on a hash. The array-based forms will be somewhat faster and smaller; the hash-based forms are more flexible.

The class created by struct must not be a subclass of another class other than UNIVERSAL.

It can, however, be used as a superclass for other classes. To facilitate this, the generated constructor method uses a two-argument blessing. Furthermore, if the class is hash-based, the key of each element is prefixed with the class name (see Perl Cookbook, Recipe 13.12).

A function named new must not be explicitly defined in a class created by struct.

The ELEMENT_LIST has the form

NAME => TYPE, ...

Each name-type pair declares one element of the struct. Each element name will be defined as an accessor method unless a method by that name is explicitly defined; in the latter case, a warning is issued if the warning flag (-w) is set.

Class::Struct can create your class at compile time. The main reason for doing this is obvious, so your class acts like every other class in Perl. Creating your class at compile time will make the order of events similar to using any other class ( or Perl module ).

There is no significant speed gain between compile time and run time class creation, there is just a new, more standard order of events.

With no argument, the accessor returns a reference to the element's whole array (whether or not the element was specified as '@' or '*@').

With one or two arguments, the first argument is an index specifying one element of the array; the second argument, if present, is assigned to the array element. If the element type is '@', the accessor returns the array element value. If the element type is '*@', a reference to the array element is returned.

As a special case, when the accessor is called with an array reference as the sole argument, this causes an assignment of the whole array element. The object reference is returned.

With no argument, the accessor returns a reference to the element's whole hash (whether or not the element was specified as '%' or '*%').

With one or two arguments, the first argument is a key specifying one element of the hash; the second argument, if present, is assigned to the hash element. If the element type is '%', the accessor returns the hash element value. If the element type is '*%', a reference to the hash element is returned.

As a special case, when the accessor is called with a hash reference as the sole argument, this causes an assignment of the whole hash element. The object reference is returned.

struct always creates a constructor called new. That constructor may take a list of initializers for the various elements of the new struct.

Each initializer is a pair of values: element name => value. The initializer value for a scalar element is just a scalar value. The initializer for an array element is an array reference. The initializer for a hash is a hash reference.

The initializer for a class element is an object of the corresponding class, or of one of it's subclasses, or a reference to a hash containing named arguments to be passed to the element's constructor.

Giving a struct element a class type that is also a struct is how structs are nested. Here, Timeval represents a time (seconds and microseconds), and Rusage has two elements, each of which is of type Timeval.

The constructor of a generated class can be passed a list of element=>value pairs, with which to initialize the struct. If no initializer is specified for a particular element, its default initialization is performed instead. Initializers for non-existent elements are silently ignored.

Note that the initializer for a nested class may be specified as an object of that class, or as a reference to a hash of initializers that are passed on to the nested struct's constructor.

Modified implicit construction of nested objects.
Now will also take an object ref instead of requiring a hash ref.
Also default initializes nested object attributes to undef, rather
than calling object constructor without args
Original over-helpfulness was fraught with problems:
* the class's constructor might not be called 'new'
* the class might not have a hash-like-arguments constructor
* the class might not have a no-argument constructor
* "recursive" data structures didn't work well:
package Person;
struct { mother => 'Person', father => 'Person'};

Modified by Casey West, 2000-11-08, v0.59.

Added the ability for compile time class creation.

Modified by Damian Conway, 1999-03-05, v0.58.

Added handling of hash-like arg list to class ctor.
Changed to two-argument blessing in ctor to support
derivation from created classes.
Added classname prefixes to keys in hash-based classes
(refer to "Perl Cookbook", Recipe 13.12 for rationale).
Corrected behaviour of accessors for '*@' and '*%' struct
elements. Package now implements documented behaviour when
returning a reference to an entire hash or array element.
Previously these were returned as a reference to a reference
to the element.

Renamed to Class::Struct and modified by Jim Miner, 1997-04-02.

members() function removed.
Documentation corrected and extended.
Use of struct() in a subclass prohibited.
User definition of accessor allowed.
Treatment of '*' in element types corrected.
Treatment of classes as element types corrected.
Class name to struct() made optional.
Diagnostic checks added.